FileFromFS (#2112)

* Context.FileFromFS added

* Context File and FileFromFS examples at README

Co-authored-by: Bo-Yi Wu <appleboy.tw@gmail.com>

context.go

@@ -925,6 +925,17 @@ func (c *Context) File(filepath string) {
 	http.ServeFile(c.Writer, c.Request, filepath)
 }
 
+// FileFromFS writes the specified file from http.FileSytem into the body stream in an efficient way.
+func (c *Context) FileFromFS(filepath string, fs http.FileSystem) {
+	defer func(old string) {
+		c.Request.URL.Path = old
+	}(c.Request.URL.Path)
+
+	c.Request.URL.Path = filepath
+
+	http.FileServer(fs).ServeHTTP(c.Writer, c.Request)
+}
+
 // FileAttachment writes the specified file into the body stream in an efficient way
 // On the client side, the file will typically be downloaded with the given filename
 func (c *Context) FileAttachment(filepath, filename string) {